I don't think your game has been solved, I am still working out that the stress options aren't as obvious as some of us may assume, but I would suggest that more stress reward be given to those who take a risk on players selected who are on the borderline of coming in or coming out or under an injury cloud.
You are already picking these well with the standard return rates, but if your rules could give more proportional reward for players taken on double and triple stress. That is if the reward for double and triple stress was multiplied by the return rate for the set double or triple stress reward amount (which you have already set on your double and triple stress reward table). Currently there is little difference in the reward for stress options, despite greatly increased risk for some players compared to others.,
I would also suggest that the triple stress reward be increased, because there maybe even a little less reward for triple stress compared to double stress if you take into account you can get 3 double stress rewards in a 6 week period and only 2 triple stress rewards. Given the triple stress is a bigger risk it should be a bigger reward than the double stress.
For instance, using your table, if I triple stress a player twice in a row from this week, and again in 3 weeks time (involving a 6 week period) I will get two triple stress bonuses totalling $25,136. But if I double stress the same player 3 times in a row (again involving the same 6 week period) I will get 3 double stress bonuses totalling $26,035.
Now I have said that, I should declare that is why I have changed from triple stress to double stress and would recommend waiting just over a week before making any of my suggested changes.